Electrolytic refining of tin



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ELEGTRULYTIC REFINMG' "OF rm.

Specification of Letters Patent.

Patented Nov. ltd, 1921.

We Elrawing. application filed hotelier it, 1918, dcrial No. $575M. Renewed Decorator t, race.

Serial lilo. lttttfidl.

To all whom it may concern:

Be it known that l, FRANK (3. Mar at s, a citizen of the United States, and resident of Bloomington, in the county of Monroe and State of lndiana, have invented certain new and useful Improvements in Electrolytic Refining of Tin, of which the followin is a specification.

he invention relates in general to an improvement in the process of producing electrolytically refined tin from impure tin cast in the form of anodes and acted upon by an electrolyte and features the situation where there is a relatively low tin content and a relatively high sulfuric acid content.

Heretofore as disclosed in thepatentto Robert L. Whitehead No. 1,157,830, dated October 26, 1915, it is proposed to produce from the impure tin which usually contains lead, antimony and other impurities, an electrolyte of such a character that it will insure the continued maintenance of the electrolytic decomposition of the tin during the refining operation. This Whitehead process consists fundamentally in maintaining at least a- 6% solution of tin in the electrolyte and in this condition the'proccss can be operated continuously when the electrolyte has in solution one-tenth of one per cent. sulfuric acid and 15-20% of hydrofluosilicic acid.

Difliculty is experienced with some grades oi? tin, such for instance as Bolivian tin which contains high percentages of impurities, when such metals are used to obtain and maintain the 6% solution of tin required by the Whitehead process. It takes time and power to practice the usual process to raise the baskets containing the tin shot into the electrolyte and even then, dificulty is experienced in obtaining such solution of tin as high as six per cent. The higher the percentage of tin required in the solution the more time is required at an increasing ratio and the greater is the dificulty of maintaining this high percentage and with some poor grades of tin it is practically impossible to maintain the 6% tin content after it has been initially obtained.

Accordingly, the primary object of the in vention is to produce pure tin electrolytically from certain grades of'impure tin anodes withan electrolyte which is o erative with a relatively low percentage ct tin content.

Further due to present war conditions, the hydrofiuosilicic acid required in the known process is dificult to obtain and has accordingly become somewhat expensive for extensive use in metallurgical processes. lzlconomically, it is an advantage to reduce the amount or hydrotluosilicic acid but wherever attempts have been made to reduce'the percentage of the hydrofiuosilicic acid to any material extentbelow the 20% suggested in the Whitehead process, and especially where the tin content is as low as 2%, there resulted on the cathode plates the formation of projections and uneven coatings, called sprouts or trees, which gave rise to short circuits and other polarizing and deteriorating actions.

Accordingly, another object of the invention is to provide an electrolyte oi the hind suggested and in which it is possible to reduce the amount of hydrofluosilicic acid used below what has heretofore been necessary, and at the same time to maintain the continuity of action during the electrolytic process free of polarizing and other objectionable results.

Broadly, ll attain these objects by introducing a new addition agent to the usual electrolyte which agent permits of a reduction of the hydrofluosilicic acid content and at the same time causes the deposition of an unusually pure tin even when the electrolyte contains as low as 2% by weight tin in content.

, Of the coercially available substances which are utilized as the-addition agent, cresylic acid gives excellent results. A. pure form of cresylic acid does not give as good results as' the more or less impure commercial term and' the best results have been obtained from the crude residue remaining in the still after the cresylic acid has been dis tilled out. This residue at present commands a high price and cannot be used commercially from an economical consideration. Certain other phenols have been used with satisfactiondair results having been obtained by substances which consists of 40% of meta cresol; 35% of .ortho cresol and. 35%

tin has been of para cresol. vCertain other substances such for instance as benzol have" been used and it is to be assumed that the beneficial agent is some substance common to all these real gents ollowlng the sequence of steps recited in the patented process above recited, the electrolyte articularl v forming the novel element 0 this disc osure, is prepared from impure tin anodes containing tin, co per,

lead, or other material. As an exam e of.

one suitable type of electrolyte a solutlon of cres lic acid about {1; of 1%,hydrofluosilicic aci about 51%, and sulfuric acid 5% by weight has given satisfactory results. An electric. current of suitable voltage and amperage is a plied until upon testing the solution has ta en up about 2% by weight of tin whereupon the passage of the current is discontinued. During this formation of the electrolyte, the sulfuric acid contained in the solution combines with the lead and certain other impurities in accordance with known chemical reactions and precipitates certain of the impurities which would otherwise go into solution as is well known in such processes. The electrolyte thus formed consists of tin dissolved in the hydrofluosilicic acid and presumably. in the cresylic acid which ormed from the impure tin anodes without bringing any of the lead or other impurities into solution. The electrolyte thus formed is utilized as an electrolyte in the refining operation. The tin is taken from the highly impuretiii anodes and deposited on the cathodes in an unusually Euro state. This cathode tin is characterized y hard, uniformly dense and crystalline structure; is free from projections and is of substantially uniform thickness. It is commercially pure, testing over 99.9%. The tin thus formed is disclosed as a new composition of matter, which composition of matter is a pure desirable for technical purposes and is of a higher grade than has been produced even from the high grade tin ores obtained from the Malay traits Settlements. The process herein disclosed can be performed and the product produced evenfrom the highly impure grades of Bolivian andSouth American ores. v

- It is comparative] easy to obtain a 2% solution of tin and t is is all that is necessary to obtain an operative electrolyte in the grese'nce of the addition agent. It is note that the amount of hydrofluosilicic acid is reduced froni'the necessary 20% recited in the Whitehead disclosure to about 5% and the process admits of the use of even a lower percentage of hydrofluosilicic acid. At the same time this process permits the use of agreater percentage of sulfuric acid than has been possible heretofore,

e of tin particularly.

percentage of sulfuric acid which won d have been objectionable in the presence of the old twenty per cent. of hydrofluosilicic acid is not objectionable inthe presenceof the low tin percentage herein suggested.

In the preceding statement no reference has been made to the use of glue as an additional reagent in the electrolyte because the process has given satisfacto results without the employment of glue. owever, if a little glue is added together with the cresol even better results are attained and in the most perfected process the use of the usual amount of glue 18 suggested.

Having thus described my invention, I claim 1. In the electrolytic refining of impure tin, the process which consists in employing as the electrolyte a solution of tin in hydrofluosilicic acid, sulfuric acid and cresylic acid and in which the tin content is approximateliy two per cent. by weight. A

2. n the electrolytic refining of impure tin, the process which consists in passing an electric current of suitable voltage and amperage from the tin anode to a cathode through an electrolyte solution containing cresylic acid and containing less than six per cent. by weight of tin in solution.

3. In the electrolytic refining of impure tin, the process which consists in paming an electric current of suitable voltage and amperage from the tin anode to a cathode through an electrolyte solution containing cresylic acid and containing approximately two r cent. by weight of tin in solution.

4. n the electrolytic refining of impure tin, the process which consists in passing an electric current of suitable voltage and-arm perage from the tin anode to a cathode through an electrolyte solution containing a solution of hydrofluosilicic acid, cresylic acid and less than six per cent. by weight of tin.

5. An electrol te for the deposition of tin comprising an e ectrolyte solution of tin in hydrofluosilicic acid in the proportions approximatelyoftwo percent. by weightof tin and five per cent. by weight of the'free acid together with'an addition agent capable of causing" the tin to deposit in a coherent form when a suitable current is passed therethrougli from an impure tin anode to a cathode.

6. In the electrolytic refining of impure tin the process of producing an appropriate electrolyte for the refini operation which consists in passing an e ectric current of suitable voltage and amperage frorn'ihe im pure tin as an anode to a cathode through a solution of hydrofluosilicic acid having a strength of less than 20% and in the press- 7 tin, the process out ence of an addition agent ence of an addition agent capable of preventing polarization and the production of trees on the cathode incidental to processes when there is a reduction in stren h of hydrouosilic ic acid used.

7. 1n the electrolyfic not: ot impure tin the process of producing an appropriate electrolyte tor the refining operation which consists in pa an electric current of suitahle voltage and amperage hem the impure tin as an anode to a cathode through a solution of hydrouosilicic acid having a strength or less than 2ll% and in the prescapahle ot preventing polarization and the production at trees on the cathode incidental to processes when there is a reduction in the 20% strength of hyofiuom licic acid used and in the presence of sulturic acid.

8. lo the electrolytic reg oi impure producing an appropriate electrolyte tor the refining operation which consists in passing an electric current of suitable voltage and amperage from the impure tin as an anode to a cathode through a solution conta w cresylic acid.

, 9. lln the electrolytic reg or impure tin, the process ct producing an appropriate electrolyte for the re operation which consists in passing an e ectric current oi suitable voltage and amperage from the impure tin as an anode to a cathode through a solution containing cresylic acid in an impure form.

10. in the electrolytic reg oi impure tin, the process of producing an appropriate electrolyte for the refining operation which consists in passing an electric current of suitable voltage and amperage from the impure tin as an anode to a cathode through a solution contag a phenol.

11. In the electrolytic refi of impure tin, the process ot producing an appropriate electrolyte tor the reg operation which consists in passing an electric current of suitable voltage and amperage from the impure as an anode to a cathode throh a solution at hydroduosilicic acid having a strength of lem than 20% and inthe presence of an addition agent coutainiuga phenol in the solution.

l2. lln the electrolytic refining of impure tin containing lead, the process of preven contamination of the tin deposited from the impure tin anode upon the cathode, which consists in employing as the electrolyte a solution of tin in hydrofiuosilicic acid, together with a protective agent suficient to convert the lead contained in the dissolving tin anode intoa compound insoluble the electrolyte and an addih on agent capahle at preventing polarization and the production of trees on the cathode. M

13. lo the electrolytic regot impure the 2695 7 tin coutag lead, the process of preventmg contamination of the tin deposited from the impure tin anode upon the cathode which consists in employing as the electrolyte a solution of tin in hydrofluosilicic acid, to-

ll. lo the electroyltic refining otimpure' containing lead, the process of preventing contamination of the tin deposited from the impure tin anode upon the cathode which consists in employing as the electrolyte a solution ot tin in hydrofluosilicic acid, together with a protectiveagcnt suilicient to convert the lead contained in the dissolving tin anode into a compound insoluble in the electrolyte and an addition agent containing cresylic acid. v

15. A composition of matteruconstituting an electrolytically refined and chemically pure tin characterized by a hard, dense and finely crystalline structure.

It. has electrolytically produced cathode characterized by a hard, uniformly dense,

Sm: structure, free from projections and of substantially uniform thickness.

l'l'. In the electrolytic refining of impure tin, the process of producing an appropriate electrolyte for the refining operation which consists in passing an electric current of suitable voltage and amperage from the impure tin as an anode to a cathode througha solution containing cresylic acid and glue. 18. lo the electrolytic refining of impure tin, the process of producing an appropriate electrolyte tor the refining operation which consists in passing an electric current of suitable voltage and amperage from the impure tin as an anode to a cathode through a solution containing a phenol and glue.

19. lo the electrolytic refining of impure containing lead, the process of preventing contamination of the tin deposited from the impure tin anode upon the cathode whlch consists in employing as the electrolyte a solution of tin in hydrofiuosilicic acid, together with a protective agent such as hydrotluosilicic acid of a strength suflicient to convert the lead contained in the dissolving tin anode into a compound insoluble in the electrolyte and an addition agent containing cresylic acid and glue.

20. lo the electrolytic refining of 1mpure tin, the process which consists in employing as the electrolyte a solution of tin, sulfuric pure tin as an anode t6 a: cathode through a solution containing a phenol sulfuric acid and a tin dissolving agent. l

22. An electrolyte for the deposition of tin 5 comprisin an electrolyte solution of tin a free acid in the proportions approximately per cent. by weight of the of two per cent. by weight of tin and five free acid together 

